The present invention relates to a water-soluble material, a chemically amplified resist and a pattern formation method using the same for use in pattern formation in fabrication process or the like for semiconductor devices.
In accordance with the increased degree of integration of semiconductor integrated circuits and downsizing of semiconductor devices, there are increasing demands for higher performance of lithography technique. In particular, in order to refine patterns, a chemically amplified resist is currently used as a resist material. In the chemically amplified resist, an acid is generated from an acid generator included therein through exposure and post exposure bake, so as to cause a reaction of the resist by using the generated acid as a catalyst. Thus, the resolution and the sensitivity in the exposure are improved.
Now, a conventional pattern formation method will be described with reference to FIGS. 7A through 7D.
First, a positive chemically amplified resist material having the following composition is prepared:
Base polymer: poly((t-butyloxycarbonylmethyloxystyrene)  2 g(65 mol %) - (hydroxystyrene) (35 mol %))Acid generator: triphenylsulfonium nonaflate0.05 gSolvent: propylene glycol monomethyl ether acetate  18 g
Next, as shown in FIG. 7A, the aforementioned chemically amplified resist material is applied on a substrate 1 so as to form a resist film 2 with a thickness of 0.4 μm.
Then, as shown in FIG. 7B, pattern exposure is carried out by irradiating the resist film 2 with exposing light 3 of KrF excimer laser with NA of 0.68 through a mask 4.
After the pattern exposure, as shown in FIG. 7C, the resist film 2 is baked with a hot plate at a temperature of 105° C. for 60 seconds (post exposure bake).
Next, the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern 2a made of an unexposed portion of the resist film 2 and having a line width of 0.14 μm is formed as shown in FIG. 7D.
As shown in FIG. 7D, however, the resist pattern 2a formed by the conventional pattern formation method has a T-top shaped defective portion designated as an insoluble skin layer 2b on the uppermost portions of the side faces thereof (for example, see O. P. Kishkovich and C. E. Larson, “Amine Control for DUV Lithography: Identifying Hidden Sources”, Proc. SPIE, 3999, 699 (2000)).
When the resist pattern 2a in such a defective shape is used for etching a target film, the resultant pattern of the target film is also in a defective shape, which disadvantageously lowers the productivity and the yield in the fabrication process for semiconductor devices.
Such an insoluble skin layer in the T-top shape is formed when a positive resist is used, and when a negative resist is used, pattern failure derived from reduction in the film thickness occurs.